Abstract: Cores from the Miocene Castor Creek Member of the Fleming Formation, Fort Polk, Louisiana: Relationship to the Outcropping Miocene Terrestrial Vertebrate Fossil-Bearing Beds

Megan H. Jones, Judith A. Schiebout, Julitta T. Kirkova

A series of clays and silty clays with well-developed paleosols were recovered from three 15m cores drilled in the Castor Creek member of the Fleming Formation in western Louisiana. These cores were taken to provide stratigraphic control for the outcropping conglomeratic beds bearing small Miocene terrestrial mammal teeth. These fine-grained core sediments and outcropping conglomeratic units were deposited in a fluvial setting.

The conglomeratic units were not penetrated by coring indicating that they are very discontinuous, localized deposits. The sedimentology and distribution of these deposits and a thin interval of poorly sorted, cross-bedded sandstone found in one core, suggest that these are coarse deposits formed at the bases of minor channels or gullies. The fine-grained core sediments are flood plain deposits. These thick sequences of massive gray clays with paleosol features such as mottles, roots, root casts, carbonate nodules and slickensides reflect deposition in well-drained, seasonally wet flood plain backswamps and lakes. Intervals of relatively unaltered parallel and wavy laminated silts and clays may represent lacustrine delta fill sequences.

Well-developed soil profiles, containing A, B, and C horizons, characterize these fine-grained sediments. Mottle coloring indicating oxidation and possible water table fluctuations is prevalent throughout the paleosols. Roots and large root burrows which characterize A horizons are abundant. Stage II carbonate development is common in most B and some C horizons. Slickensides, resulting from the alternating wetting and drying of soils, are common. In general, these paleosol features support the interpretation of a well-drained, seasonally wet fluvial setting.

AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana